1. Field of the Invention
The present invention relates generally to cabling and cabling systems, and more particularly to a universal cabling system wherein the requirement for specific wire interconnections between first and second devices is accomplished through use of a programmable I/O module for making connection to the first device, and directing connections from the first device to selected wires of a cable for connection to the second device.
2. Description of the Prior Art
Complex electrical/electronic systems often require custom cable configurations. Cables are usually special configurations for a particular application. Even in relatively simple systems such as home audio and small computer systems, a number of different cables are typically required. In larger applications, such as industrial control systems, the number of custom cable designs is extensive. In industrial control systems such as those that run automotive plants, etc., interaction is required between control apparatus and sensors and actuators. The apparatus providing the corresponding connections will be referred to as input and output systems. Through the output system, the control system can turn on lights, pumps, valves and other devices. Similarly, through the input system, the control system can sense the state of a pushbutton, whether a switch is on or off, or whether a tank is full or how fast a shaft is turning.
In prior art control systems, such as a Programmable Logic Controller (PLC), the user of the control system electrically connects the sensors and actuators to the input/output systems using individual wire connections or via connectorized wire harnesses. A common method of connecting sensors and actuators to industrial control systems is through the use of individual wire connections via terminal blocks. Terminal blocks usually employ a screw-driven clamp. An electrical wire's insulation is removed from the end, and then the bare wire is slid under the screw-driven clamp. The screw is then tightened to secure the wire under the clamp and effect an electrical connection between the wire and the terminal block. Increasingly, various spring clamps are used to hold the wire, but these are essentially the same as screw-driven clamps. FIG. 1 shows how individual wires 10 are connected to the input and output Modules 12, 14 of a PLC 16 through terminal blocks 18 to three devices, a light bulb 20, a switch 22 and a proximity switch 24. A proximity switch is a common type of switch that can detect the presence (typically) of metal, and gives an indication by interrupting or passing electrical current.
A disadvantage of the method illustrated in FIG. 1 is that the terminals 26, 28 on the input or output modules of the PLC 16 are not necessarily conveniently arranged for facilitating easy connection of a load, such as a light bulb or switch. As a result, a great deal of custom, hand-wiring must be performed in order to effect the interconnections. In addition the electricity, from a supply 30 to power certain actuators and sensors such as the light bulb or proximity sensor, must be provided on the terminal blocks 18 in order to make connections to the light bulb or switch. In general, the prior art output Modules 12 and 14 do not supply power to the load, they only switch the power. The custom wiring design and implementation illustrated in FIG. 1 significantly adds to the cost and size of the system.
Another method of connecting an industrial control system such as a PLC to a load is via a connectorized wire harness or cable. FIG. 2 shows one input module 32 and one output module 34 from a PLC 36. The input/output modules 32 and 34 are equipped with connectors 38 and 40 respectively that allow cables 42 and 44 to be used to make connection with various sensors and actuators. Unfortunately, the cable from the input or output module cannot generally connect directly to the sensor or actuator because the connectors 38 and 40 on the PLC 36 are rarely configured to accept a sensor signal or provide the actuator power. For this reason, FIG. 3 represents the most common method of connecting a PLC to a sensor or actuator when employing connectors on the PLC. In FIG. 3, cables 40 from the PLC input 32 and output 34 modules connect to circuit boards 46 and 48 which contain terminal blocks 50 for making connections to the control system. Therefore, even when connectorized cables are employed, the prior art still requires making connections through use of individual wire connections such as terminal blocks.
Making a direct connection between a PLC and a sensor or actuator without individual wire connections is problematical. An example situation is when a PLC must be connected to a device that already is equipped with a connector. The need to connect a PLC to such a device is very common. A typical device is a mass flow controller equipped with a connector for connecting signals that must be connected to the PLC. In this case, the connections are complicated by the fact that the PLC output module contains only outputs and the PLC input module contains only inputs, whereas the mass flow controller connector contains signals that represent both inputs and outputs. To make matters worse, some of the signals are discrete—that is, on/off—and some are continuously varying analog signals. In addition, the mass flow controller also requires application of a power supply voltage and return/ground to the flow controller connector.
In general, prior art methods and apparatus require the use of custom cable harnesses designed and built to connect the rigid format of a PLC to the varying formats of the disparate devices such as mass flow controllers and power supplies. The difficulty of designing, fabricating and installing complex wire harnesses is so great that the predominant method of connecting PLC's to sensors and actuators is via individual wire connections and terminal blocks.
FIGS. 4a and 4b show two examples of typical non-standard cable construction. In FIG. 4a each of wires 52 and 54 connects to a different pin on connector 56 than on connector 58. The cable of FIG. 4b has two connectors 60 and 62 on one end and a single connector 64 on the other end.